The present invention pertains to an apparatus for monitoring the speed and lateral position variations of a rotating shaft of a coolant circulating pump for a nuclear steam supply system.
In a nuclear steam supply system, coolant is circulated through the reactor by means of one or more large, high speed reactor coolant pumps. Loss of reactor coolant has serious adverse consequences, including, at a minimum, reactor shutdown and, possibly, reactor core damage. Due to the criticality of continued coolant supply, it is now a regulatory requirement that at least the rotational speeds of the coolant pump shafts be continuously monitored.
The problem of nuclear shaft monitoring system pump is made vastly more complex by radioactivity which degrades the performance of any electronic equipment emplaced in the pump area. At the present time, such monitoring is performed by a magnetic reluctance device which detects and counts the passage, through a detection gap, of the teeth of a metallic gear mounted on the pump shaft. Devices of this type suffer, however, in that they require frequent recalibration which must be performed with the pump in operation. Unfortunately, due to the radioactivity present during reactor operation, such recalibration can only be performed during system outages.
Further, given the severe consequences of coolant pump failure, it would be advantageous to have the ability to predict shaft failure sufficiently in advance to permit repair or replacement during a regularly scheduled system outage. Since shaft failure is almost invariably preceded by increased shaft wobble or lateral position variation, the ability to monitor the magnitude of such wobble and detect increases therein would provide a basis for such failure prediction.
It is, therefore, an object of the present invention to provide an apparatus for monitoring the rotational speed of the shaft of a coolant circulating pump in a nuclear steam generating system, which also monitors shaft wobble.
It is yet another object of the invention to provide such an apparatus which is accurate, reliable and immune to radiation damage.
The foregoing and other objects and advantages of the invention as may hereinafter appear are achieved, in general, by an apparatus comprising a light source for sequentially directing a single light beam at at least one, but preferably a plurality, of light reflecting surfaces formed on the shaft and light receiving means for sequentially receiving a pair of spaced apart light beams reflected off the reflective surfaces. The intensity of the two light beams of the pair is measured, on a time-dependent basis, by an intensity measuring means connected to the light receiving means by fiber optic cable. A processor calculates the shaft rotational speed and the magnitude of the shaft wobble or lateral position variation from a nominal lateral position as functions of the time-dependent measurements of the pair of reflected light beams.
More specifically, the light receiving means and the intensity measuring means are so positioned and adjusted that the pair of light beams are of equal indicated intensity when the shaft is in its nominal lateral position.
Advantageously, the reflective surfaces are defined by at least one but preferably a plurality, of axially extending non-reflective stripes formed on the polished shaft surface. Also advantageously, the light receiving means and the intensity measuring means are connected by fiber optic cables.